1. Field of the Invention
The present invention relates to surface mount type antennas in which a radiation electrode is provided on a substrate, and radio transmitters and receivers including such surface mount type antennas.
2. Description of the Related Art
FIG. 8A shows an example of a typical antenna. An antenna 30 is disclosed in European Patent Laid-Open No. EP0938158A2, and includes a conductor line 31. One end of the conductor line 31 defines a fed-end section connected to the signal source (transmission and receiving circuit) 32 of a radio transmitter and receiver, such as a portable telephone, and the other end defines an open end. The conductor line 31 is bent in a loop manner, and the open end xcex2 of the conductor line 31 is disposed in the vicinity of the fed-end-section side xcex1 with a gap therebetween.
The antenna 30 has a return-loss characteristic similar to that shown in FIG. 8B. More specifically, in the antenna 30, the conductor line 31 resonates at resonant frequencies F1 and F2 to execute an antenna operation according to a signal sent from the signal source 32. Among a plurality of resonant frequencies of the conductor line 31, a resonant operation at the lowest resonant frequency is called a basic mode, and a resonant operation at a higher resonant frequency than that of the basic mode is called a high-order mode.
In the antenna 30, the high-order-mode resonant frequency F2 is variably controlled, with the basic-mode resonant frequency F1 being rarely changed when the capacity between the fed-end-section side xcex1 and the open end xcex2 of the conductor line 31 is variably controlled to variably change the amount of electromagnetic coupling between the fed-end-section side xcex1 and the open end xcex2. Therefore, in the antenna 30, the basic-mode resonant frequency F1 and the high-order-mode resonant frequency F2 are easily adjusted to desired frequencies.
Recently, very compact antennas have been demanded for portable telephones and global positioning systems (GPSs). Because the antenna 30 includes the conductor line 31, and the conductor line 31 must have a length corresponding to the specified basic-mode resonant frequency, however, it is difficult to reduce the size of such antennas and it is very difficult to successfully satisfy the recent demand for reducing the size of such antennas.
In addition, since the antenna 30 includes only the conductor line 31, it is difficult to prevent the size of the antenna 30 from increasing while its frequency band is expanded.
In order to overcome the above-described problems, preferred embodiments of the present invention provide a surface mount type antenna having a reduced size and a wide frequency band, and a radio transmitter and receiver including such a novel antenna.
One preferred embodiment of the present invention provides a surface mount type antenna including a fed radiation electrode to which a signal is sent from a signal source that is provided on a substrate, wherein one or a plurality of fed radiation electrodes each having a loop shape in which a first end defining a fed-end-section which receives a signal from the signal source is disposed opposite the other end which defines an open end, with a gap disposed therebetween is provided, and in addition, a non-fed radiation electrode which is electromagnetically coupled with at least an adjacent fed radiation electrode to generate a double-resonant state is provided on the substrate.
The surface mount type antenna is preferably configured such that the non-fed radiation electrode includes one ground end connected to the ground and another open end, and one or a plurality of non-fed radiation electrodes each having a loop shape in which the open end is disposed opposite a ground-end side with a gap disposed therebetween is formed.
The surface mount type antenna is preferably configured such that the fed radiation electrode and the non-fed radiation electrode perform a basic-mode resonant operation and a high-order-mode resonant operation having a higher resonant frequency than in the basic mode, and the distance between the open end of the loop-shaped fed radiation electrode or the loop-shaped non-fed radiation electrode and a portion opposite the open end through a gap is changed to adjust the capacitance of a capacitor generated between the open end and the portion opposite the open end to that corresponding to a specified high-order-mode resonant frequency.
The surface mount type antenna is preferably configured such that the loop-shaped fed radiation electrode or the loop-shaped non-fed radiation electrode has a loop shape by providing a slit for a plane-shaped pattern, and the slit is folded one or more times, or has a bent shape.
The surface mount type antenna is preferably configured such that the substrate is a dielectric substrate, and the dielectric substrate defines a coupling-amount adjusting element for adjusting the amount of coupling between the fed radiation electrode and the non-fed radiation electrode by the dielectric constant of the substrate.
The surface mount type antenna is preferably configured such that the fed radiation electrode and the non-fed radiation electrode perform a basic-mode resonant operation and a high-order-mode resonant operation having a higher resonant frequency than in the basic mode. The substrate is a dielectric substrate, and the dielectric substrate functions as open-end-capacitor adjusting element for adjusting the capacitance of a capacitor provided between the open end of the loop-shaped fed radiation electrode or the loop-shaped non-fed radiation electrode and a portion opposite the open end by the dielectric constant of the substrate to adjust the high-order-mode resonant frequency.
Additionally, the surface mount type antenna is preferably configured such that one or both of a capacity-loaded electrode disposed through a gap adjacently to the fed radiation electrode and having a capacitor between itself and the fed radiation electrode and a capacity-loaded electrode disposed through a gap adjacently to the non-fed radiation electrode and having a capacitor between itself and the non-fed radiation electrode are provided, and the capacity-loaded electrode(s) is electrically connected to the ground.
Another preferred embodiment of the present invention provides a radio transmitter and receiver including one of the surface mount type antennas according to preferred embodiments described above.
In various preferred embodiments of the present invention, since a surface mount type antenna includes a fed radiation electrode provided on a substrate, the antenna is much more compact than the line-shaped antenna shown in the conventional example. On the substrate, a non-fed radiation electrode is disposed in the vicinity of the fed radiation electrode and is electromagnetically coupled with the fed radiation electrode to generate a double-resonant state. Double resonance caused by the fed radiation electrode and the non-fed radiation electrode can easily extend the frequency band. Therefore, an antenna and a radio transmitter and receiver having a greatly reduced size and a wide frequency band are obtained.
According to preferred embodiments of the present invention, since, on a substrate, a loop-shaped fed radiation electrode is provided and a non-fed radiation electrode is also provided to generate a double-resonant state together with the fed radiation electrode, the antenna is made much more compact than the line-shaped antenna, shown in a conventional example, and the frequency band thereof is easily expanded. Therefore, the surface mount type antenna and the radio transmitter and receiver having a greatly reduced size and an extended frequency band are provided.
When a non-fed radiation electrode has a loop shape, the capacitance of a capacitor defined between an open end and a ground end side of the non-fed radiation electrode is adjusted to easily adjust the high-order-mode resonant frequency without changing the basic-mode resonant frequency, as in a fed radiation electrode. Therefore, the basic-mode and high-order-mode resonant frequencies of the fed radiation electrode and the non-fed radiation electrode are easily adjusted such that, for example, electromagnetic waves can be transmitted and received in frequency bands corresponding to a plurality of communication systems, thus easily implementing a multiple-frequency-band antenna.
Since a fed radiation electrode or a non-fed radiation electrode has a loop shape, its electric field is confined to an area where the fed radiation electrode or the non-fed radiation electrode is provided. Therefore, a narrow frequency band and a reduction in gain caused when the electric field is caught at the ground side are effectively prevented. Such a narrowed frequency band and a reduction in gain are especially likely to occur at a high-order-mode side. The loop-shaped electrode prevents this problem from occurring.
In addition, since the electric field is shut in the area where the fed radiation electrode or the non-fed radiation electrode is formed, the amount of electromagnetic coupling between the fed radiation electrode and the non-fed radiation electrode is easily controlled.
Further, when a plurality of fed radiation electrodes is formed, mutual interference among the plurality of fed radiation electrodes may cause a problem. Because a loop-shaped fed radiation electrode confines an electric field, mutual interference with the loop-shaped fed radiation electrode is suppressed, and the independence of the resonant operation of each fed radiation electrode is greatly increased.
Furthermore, since the electric field is confined, the antenna is unlikely to receive external effects. When a ground object approaches or moves away from the surface mount type antenna, for example, characteristic fluctuations caused by the movement of the object are effectively suppressed.
When a slit is provided in a plane-shaped pattern to form a loop-shaped radiation electrode, the radiation electrode has a larger area than when the loop-shaped radiation electrode is formed by a line-shaped pattern.
When a substrate is a dielectric substrate and it functions as a coupling-amount adjusting element, the adjustment of the distance between a fed radiation electrode and a non-fed radiation electrode, and a change in the dielectric constant of the dielectric substrate adjust the amount of electromagnetic coupling between the fed radiation electrode and the non-fed radiation electrode. Therefore, while the size of the antenna is not increased, the amount of electromagnetic coupling between the fed radiation electrode and the non-fed radiation electrode can be adjusted such that the fed radiation electrode and the non-fed radiation electrode generate a successful double-resonant state, which extends the frequency band.
When the capacitance of a capacitor generated between an open end and a fed-end-section side of a fed radiation electrode is adjusted by the dielectric constant of the dielectric substrate, or when the capacitance of a capacitor formed between an open end and a ground-end-section side of a non-fed radiation electrode is adjusted by the dielectric constant of the dielectric substrate, the high-order-mode resonant frequency of the fed radiation electrode or the non-fed radiation electrode is easily adjusted without changing the shape and size of the fed radiation electrode or the non-fed radiation electrode, that is, without increasing the size of the antenna. In addition, the variable range of the high-order-mode resonant frequency is greatly extended.
When a capacity-loaded electrode to be grounded is arranged in the vicinity of a fed radiation electrode or a non-fed radiation electrode with a capacitor generated therebetween, if the capacitance of the capacitor generated between the fed radiation electrode or the non-fed radiation electrode and the capacity-loaded electrode is variable, the capacitance of a capacitor generated between the fed radiation electrode or the non-fed radiation electrode and the ground is changed to adjust a resonant frequency of the fed radiation electrode and the non-fed radiation electrode. Therefore, the resonant frequency is adjusted much more easily.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.